The present invention relates generally to the field of radio frequency identification (RFID) devices or tags and specifically to RFID devices which provide distinct non-interacting protocol variants to minimize interactions between RFID devices used for different purposes.
RFID transponders (commonly referred to herein as “tags”) in the form of labels, inlays, straps or other forms are widely used to associate an object with an identification code. Tags generally include one or more antennas with analog and/or digital electronic circuits that include communications electronics (such as an RF transceiver), data memory (for storing one or more identification codes), processing logic (such as a microcontroller) and one or more state storage devices. Examples of applications that can use RFID tags include luggage tracking, inventory control or tracking (such as in a warehouse), parcel tracking, access control to buildings or vehicles, etc.
There are three basic types of RFID tags. A passive tag is a beam powered device which rectifies energy required for operation from radio waves generated by a reader. For communication, the passive tag creates a change in reflectivity of the field which is reflected to and read by the reader. This is commonly referred to as continuous wave backscattering. A battery-powered semi-passive tag also receives and reflects radio waves from the reader; however a battery powers the tag independent of receiving power from the reader. An active tag, having an independent power supply, includes its own radio frequency source for transmission.
The reader, sometimes referred to as an interrogator, includes a transmitter to transmit RF signals to the tag and a receiver to receive tag modulated information. The transmitter and receiver can be combined as a transceiver which can use one or more antennas. Communications between a reader and tag is defined by an air interface protocol, such as (without limitation):
(i) EPCglobal's EPC Radio-Frequency Identity Protocols Class-1 Generation-2 UHF RFID Protocol for Communications at 860 MHz-960 MHz, version 1.2.0 (http://www.epcglobalinc.org/) (hereinafter referred to as the “UHF Gen2 standard”);
(ii) adaptations of the UHF Gen2 standard for operation at high frequency (“HF”), for example at 13.56 MHz; and
(iii) ISO/IEC 18000-6 Information technology—Radio frequency identification for item management—Part 6: Parameters for air interface communications at 860 MHz to 960 MHz, Amendment 1: Extension with Type C and update of Types A and B. Each of the above protocols is incorporated herein by reference for all purposes.
Multiple wireless tags can be interrogated by sending a code from an interrogating transmitter (e.g., a reader) and having information transmitted by the tag in response. This is commonly accomplished by having the tag listen for an interrogation message and for it to respond with a unique serial number and/or other information. The tags typically have limited power available for transmitting data wirelessly to the reader. It is desirable to extend the range of wireless tags so that it is not necessary to bring each tag close to a reader for reading. However, when the range of the reading system is extended, many tags will be within the range of the interrogating system so that their replies may corrupt each other.
Prior art attempts to avoid collisions when reading multiple RF tags are described in U.S. Pat. Nos. 5,266,925; 5,883,582; 6,072,801; and 7,716,208. However, these prior art approaches provide a protocol in which readers for each of these protocols interact with all tags using that same protocol. Often this is desirable, leading to standardized tags and readers which can allow users of RFID systems to purchase components of systems from many different providers, and read tags which come from many different sources or suppliers of goods.
In some cases, however, it is desired by users of RFID systems to have tags and readers which do not interact outside a specific use model. For example, launderers of clothing for industrial health, or clean room garments may want to use low cost, standardized RFID tags, readers, and systems, but do not desire to have their workers wearing the clothes tracked by RFID readers installed in stores to track products in the store's inventory. It is therefore desirable to have low cost standardized RFID products which are nonetheless non-interacting with other RFID systems, tags, and readers.